Not that they will trip, but "trip free" (Very important!), not all breakers will trip free, meaning that the handle can be held closed and the breaker mechinism will still trip free of the handle. Not all breakers will.
If they aren't "trip free", they must be very old. The requirement has been in 240-80 since the '68 code or before. Maybe much before that. The oldest code I have is the '71 and there is no vertical change line next to that section in the 71 code.
Don
edited to correct spelling
[This message has been edited by resqcapt19 (edited 10-21-2004).]